1. Field of the Invention
The invention generally relates to a voltage source circuit, and more particularly, to a self-adjustment voltage source circuit for a crystal oscillation circuit.
2. Description of Related Art
An oscillator is frequently used in semiconductor technologies as a timing module, a logic gate, and an oscillator chip, etc. A conventional oscillator includes a quartz crystal attached to a pair of capacitors having an initial resistor. The RC circuit formed by the capacitors and resistors can help adjust a timing of the oscillator. An oscillator buffer and the quartz crystal are parallel-connected. By generating an amplified and inverted signal, the conventional oscillator buffer operates like an inverter. The quartz oscillator, the RC circuit, and the oscillator buffer provides a predetermined waveform at a predetermined frequency.
The power dissipation of the oscillator may be determined by an operating frequency, a capacitor, and a work voltage of the oscillator buffer. Typically speaking, the power of the oscillator needs to be maintained at a small value. Since the pre-set operating frequency and the capacitance of the capacitor are fixed, thus to decrease power dissipation, the operating voltage of the oscillator buffer may be considered. Due to the signal bandwidth of the oscillator buffer, the amplifying gain varies with changes of the operating voltages, the process parameters, and the capacitors. However, in many practical applications, this gain variation frequently results in a long oscillation trigger time, or the crystal oscillation circuit may even fail to oscillate. Therefore, to ensure the oscillator operates normally, the work voltage of the oscillator buffer is set at a higher value to accommodate process variation, although this setting may cause unnecessary power dissipation at normal circumstance.